The invention relates to a control method and a numerical control for the vibration-reduced acceleration of the movable machine element of a numerically controlled industrial processing machine such as a machine tool, a robot or the like, wherein a path of movement of the machine element is broken down into directly successive interpolatable movement sections. The invention further relates to a numerical control for carrying out said control method.
During control of the movement of movable machine elements of industrial processing machines, the structure of the machine tends to vibrate when accelerating on account of the acceleration jolt. To preserve the mechanical parts of the processing machine, for example a numerically controlled machine tool or a robot, and to achieve an improved surface quality, for example of a workpiece to be finished, it is important to avoid machine vibrations.
Known methods of reducing this vibration tendency use a jolt limitation. Such a jolt limitation may comprise, for example, a trapezoidal acceleration profile. International patent application WO 96/12992, entitled xe2x80x9cVelocity control with limited joltingxe2x80x9d discloses a control method in which control data are read in a multi-block handling procedure. Prescribed desired speeds are approached as upper speed limits to be maintained as far as possible, and local speed limitations are approached in the form of target speeds at defined target points within the scope of a xe2x80x9clook-aheadxe2x80x9d procedure, with small acceleration changes within the limits of the maximum permissible jolt.
The use of a jolt filter which always intervenes actively in the acceleration process is also known. However, a disadvantage of such a jolt filter is that it remains active in phases in which it is not required. Furthermore, with a jolt filter, only the amplitude of a vibrational excitation is reduced, while the frequency is not completely filtered out, which leads to drastic time losses during positioning.
It is therefore the object of the present invention to develop an acceleration control that avoids excitation of machine vibration without time losses occurring in uncritical acceleration phases.
According to the present invention, this object is achieved by a control method for the vibration-reduced acceleration of a movable machine element of a numerically controlled industrial processing machine such as a machine tool, a robot or the like, wherein a path of movement of the machine element is broken down into directly successive interpolatable movement sections. The control method is designed in such a way that, during interpolation, resultant acceleration profiles which lie in a range close to a critical natural frequency of the machine element or of the machine are carried out with reduced acceleration. Acceleration control according to the present invention successfully avoids the excitation of machine vibration because the interpolator takes into account the critical natural frequency and, in the case of acceleration profiles which lie in the proximity of the natural frequency, carries out these profiles with a reduced acceleration. This is based on the realisation that overshooting of a machine element, for example a machine axis, during positioning is not at its greatest during a positioning operation from rapid traversing speed but during positioning from much slower speeds.
The object according to the present invention is also achieved by a numerical control for the vibration-reduced acceleration of the movable machine elements of a numerically controlled industrial processing machine, in which an interpolator is provided for the interpolation of a path of movement of the machine element broken down into directly successive interpolatable movement sections. The interpolator is designed in such a way that, in the interpolation, it carries out resultant acceleration profiles which lie in a range close to a critical natural frequency of the machine element, or of the machine, with a reduced acceleration.
It is particularly advantageous if the lowest natural frequency of the machine element or of the machine is taken as the critical natural frequency. It is even more advantageous if the lowest natural frequency of a machine axis or of the machine foundation bed is chosen. Furthermore, a particularly good limitation of vibrations is achieved if the acceleration is reduced to at least 90% of the maximum possible acceleration or of the nominal acceleration.